AS isn't going to buy used 757s, or whatever, for a few days a year of strong headwinds. Boeing isn't making 757s any more, and there's a reason for that: airlines can't afford over-engineered 757s for the 5% of 737 potential missions (strong headwinds on transcons/HI routes, high and hot) where 737s have some issues, given the costs for the other 95% of missions where the 737 blows the 757 away in terms of CASM.

So, no, they aren't a bad idea, given that 757s are much more likely to lose money for an operator like AS flying to HI than a 737NG is- unless your argument is that AS is better off losing money but flying more powerful planes for the rare instances where a 737 won't do.